* ???? (chenliang0...@icloud.com) wrote:
>
> ?? 2014??4??8????????10:29??Dr. David Alan Gilbert (git)
> <dgilb...@redhat.com> ??????
>
> > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
> >
> > Make qemu_peek_buffer repeatedly call fill_buffer until it gets
> > all the data it requires, or until there is an error.
> >
> > At the moment, qemu_peek_buffer will try one qemu_fill_buffer if there
> > isn't enough data waiting, however the kernel is entitled to return
> > just a few bytes, and still leave qemu_peek_buffer with less bytes
> > than it needed. I've seen this fail in a dev world, and I think it
> > could theoretically fail in the peeking of the subsection headers in
> > the current world.
> hmm, I also have got some errors(infrequently). Maybe It is one point.
> Could you show some messages about the error?
I've only seen the errors in my visitor/ber world where I use the peek_buffer
a lot more; but the one place it is used in the existing code is in
the code to check if we have the start of a subsection; if that goes wrong
I'm not sure what error would be produced.
Dave
>
> However, this patch avoids one potential issue, thanks.
>
> Reviewed-by: ChenLiang <chenliang0...@icloud.com>
> >
> > Comment qemu_peek_byte to point out it's not guaranteed to work for
> > non-continuous peeks
> >
> > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> > ---
> >
> > v4:
> > Limit the size qemu_get_buffer passes to qemu_fill_buffer on each loop
> >
> > v3:
> > Make qemu_fill_buffer return ssize_t
> > Remove the other size_t cleanup from this patch - I'll get back to them
> > later
> > Comment additions/cleanups from review
> > Stretch my -ve
> >
> > include/migration/qemu-file.h | 5 ++++
> > qemu-file.c | 53
> > +++++++++++++++++++++++++++++++++++++++----
> > 2 files changed, 54 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/migration/qemu-file.h b/include/migration/qemu-file.h
> > index a191fb6..c90f529 100644
> > --- a/include/migration/qemu-file.h
> > +++ b/include/migration/qemu-file.h
> > @@ -123,6 +123,11 @@ void qemu_put_be32(QEMUFile *f, unsigned int v);
> > void qemu_put_be64(QEMUFile *f, uint64_t v);
> > int qemu_peek_buffer(QEMUFile *f, uint8_t *buf, int size, size_t offset);
> > int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int size);
> > +/*
> > + * Note that you can only peek continuous bytes from where the current
> > pointer
> > + * is; you aren't guaranteed to be able to peak to +n bytes unless you've
> > + * previously peeked +n-1.
> > + */
> > int qemu_peek_byte(QEMUFile *f, int offset);
> > int qemu_get_byte(QEMUFile *f);
> > void qemu_file_skip(QEMUFile *f, int size);
> > diff --git a/qemu-file.c b/qemu-file.c
> > index e5ec798..6ae37d0 100644
> > --- a/qemu-file.c
> > +++ b/qemu-file.c
> > @@ -529,7 +529,15 @@ size_t ram_control_save_page(QEMUFile *f, ram_addr_t
> > block_offset,
> > return RAM_SAVE_CONTROL_NOT_SUPP;
> > }
> >
> > -static void qemu_fill_buffer(QEMUFile *f)
> > +/*
> > + * Attempt to fill the buffer from the underlying file
> > + * Returns the number of bytes read, or negative value for an error.
> > + *
> > + * Note that it can return a partially full buffer even in a not error/not
> > EOF
> > + * case if the underlying file descriptor gives a short read, and that can
> > + * happen even on a blocking fd.
> > + */
> > +static ssize_t qemu_fill_buffer(QEMUFile *f)
> > {
> > int len;
> > int pending;
> > @@ -553,6 +561,8 @@ static void qemu_fill_buffer(QEMUFile *f)
> > } else if (len != -EAGAIN) {
> > qemu_file_set_error(f, len);
> > }
> > +
> > + return len;
> > }
> >
> > int qemu_get_fd(QEMUFile *f)
> > @@ -683,17 +693,39 @@ void qemu_file_skip(QEMUFile *f, int size)
> > }
> > }
> >
> > +/*
> > + * Read 'size' bytes from file (at 'offset') into buf without moving the
> > + * pointer.
> > + *
> > + * It will return size bytes unless there was an error, in which case it
> > will
> > + * return as many as it managed to read (assuming blocking fd's which
> > + * all current QEMUFile are)
> > + */
> > int qemu_peek_buffer(QEMUFile *f, uint8_t *buf, int size, size_t offset)
> > {
> > int pending;
> > int index;
> >
> > assert(!qemu_file_is_writable(f));
> > + assert(offset < IO_BUF_SIZE);
> > + assert(size <= IO_BUF_SIZE - offset);
> >
> > + /* The 1st byte to read from */
> > index = f->buf_index + offset;
> > + /* The number of available bytes starting at index */
> > pending = f->buf_size - index;
> > - if (pending < size) {
> > - qemu_fill_buffer(f);
> > +
> > + /*
> > + * qemu_fill_buffer might return just a few bytes, even when there
> > isn't
> > + * an error, so loop collecting them until we get enough.
> > + */
> > + while (pending < size) {
> > + int received = qemu_fill_buffer(f);
> > +
> > + if (received <= 0) {
> > + break;
> > + }
> > +
> > index = f->buf_index + offset;
> > pending = f->buf_size - index;
> > }
> > @@ -709,6 +741,14 @@ int qemu_peek_buffer(QEMUFile *f, uint8_t *buf, int
> > size, size_t offset)
> > return size;
> > }
> >
> > +/*
> > + * Read 'size' bytes of data from the file into buf.
> > + * 'size' can be larger than the internal buffer.
> > + *
> > + * It will return size bytes unless there was an error, in which case it
> > will
> > + * return as many as it managed to read (assuming blocking fd's which
> > + * all current QEMUFile are)
> > + */
> > int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int size)
> > {
> > int pending = size;
> > @@ -717,7 +757,7 @@ int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int size)
> > while (pending > 0) {
> > int res;
> >
> > - res = qemu_peek_buffer(f, buf, pending, 0);
> > + res = qemu_peek_buffer(f, buf, MIN(pending, IO_BUF_SIZE), 0);
> > if (res == 0) {
> > return done;
> > }
> > @@ -729,11 +769,16 @@ int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int
> > size)
> > return done;
> > }
> >
> > +/*
> > + * Peeks a single byte from the buffer; this isn't guaranteed to work if
> > + * offset leaves a gap after the previous read/peeked data.
> > + */
> > int qemu_peek_byte(QEMUFile *f, int offset)
> > {
> > int index = f->buf_index + offset;
> >
> > assert(!qemu_file_is_writable(f));
> > + assert(offset < IO_BUF_SIZE);
> >
> > if (index >= f->buf_size) {
> > qemu_fill_buffer(f);
> > --
> > 1.9.0
> >
> >
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
